Chenodeoxycholic acid is one of the acids occurring naturally in the bile of humans and other warm blooded animals. Chenodeoxycholic acid in forms heretofore obtainable is known to dissolve gallstones, which consist of cholesterol, and has therefore been recognized as an important compound in human medicine. However, to be suitable for human therapeutic use, chenodeoxycholic acid must be available in very pure form. Human therapy, as in treatment for gallstones, requires that the compound be administered over protracted time periods, and presence of even small impurities, or of an inhomogeneity of the active compound, may lead to undesirable side effects and the symptoms accompanying the side effects. For example, liver toxicity has been observed as a result of lithocholic acid, which can occur as an impurity in chenodeoxycholic acid preparations of the prior art.
Chenodeoxycholic acid has been produced from natural starting materials. Thus, the cholic acid is esterified in the cholic acid fraction of the gall, the 3- and 7-hydroxy groups are then partially acetylated, and the free 12-hydroxy group is oxidized with chromic acid to the keto group. The 12-keto compound is heated over an extended period to temperatures of about 200.degree. C. in the presence of hydrazine hydrate and potassium hydroxide in ethylene glycol. So produced, the crude chenodeoxycholic acid contains a number of by-products which can be separated only with great difficulty, and the ultimate product exhibits an amorphous glasslike condition so as to be very difficult to crystallize.
Attempts to purify the crude chenodeoxycholic acid material by chromatographic procedures, via the methyl ester with ethyl acetate-benzene mixtures as eluents, have been reported (Acta Chemica Scandinavica 17, 1963, pages 173-186). Purification has also been attempted by way of production and isolation of the sodium salt, conversion of the salt into the acid, and subsequent recrystallization from ethyl acetate-heptane (J. Am. Chem. Soc. 72, 1950, page 5530). But both procedures lead to poor yields of products of low purity.
West German patent application No. (OS) 2,302,744 describes an attempted purification in which the raw chenodeoxycholic acid is treated in methanolic solution with a calcium or strontium salt, the corresponding chenodeoxycholic acid salt being precipitated. After separation, the salt is acidified and the chenodeoxycholic acid product extracted. There, purity of the product was characterized chromatographically and no melting point is reported. West German Pat. No. 2,404,102 describes the purification of crude chenodeoxycholic acid in the form of its aqueous alkali salt, preferably the sodium or potassium salt, which is treated with an organic solvent, preferably ethyl acetate or a mixture of isobutanol and toluene, and the salt solution is then acidified with a dilute acid, preferably hydrochloric acid, then extracted, and the chenodeoxycholic acid product is then precipitated with water. The product is reported to have a melting range of 143.degree.-146.degree. C.
It has been postulated (The Lancet, 1974, page 1518) that a very pure chenodeoxycholic acid will exhibit a melting point of 168.degree. C., but no way to produce such a material and no further criteria for its characterization have been disclosed.
X-ray investigations of the structures for the chenodeoxyycholic acid substances heretofore described have shown that the products are either X-ray-amorphous or else merely have microcrystalline partial areas which do not produce and characteristic X-ray diffraction spectra. Thus, none of the prior-art products have been of the high purity necessary for human therapeutic use, and there has been a critical continuing need for such a product.